Look at the top 7 cards from your deck. Choose a Basic Pokémon or Evolution card from those cards, show it to your opponent, and put it into your hand. Put the other 6 cards back on top of your deck. Shuffle your deck afterward.

Do Nothing

At the beginning of your turn, flip a coin. If heads, you can do nothing during your turn. If tails, your opponent can do nothing during his or her next turn.

Trivia

Both the Gym Challenge and Expedition Base Set prints of this card have a clause that reads "show it your opponent". It should read "show it to your opponent". The EX Deoxys print fixes this error.

Origin

The Master Ball is a type of Poké Ball in the Pokémon games notable for having a 100% chance of catching the Pokémon it is used on. Its inclusion as an Ace Spec card is particularly fitting as only one is ever encountered through normal gameplay, with additional copies usually requiring ownership of Pokémon with many different Original Trainers or extreme luck in an in-game lottery to obtain without external intervention such as a trade or event.